health_metric: add tmp storage support

Add the tmp storage support in health config parser and health metric.

Change-Id: Ibb265c28b22d786031ed152d2cc52f40814be984
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/health_metric_config.hpp b/health_metric_config.hpp
index 2b0a578..49f39ad 100644
--- a/health_metric_config.hpp
+++ b/health_metric_config.hpp
@@ -37,6 +37,7 @@
     memoryTotal,
     // Storage subtypes
     storageReadWrite,
+    storageTmp,
     NA
 };